The purpose of this study is twofold; namely, 1) to evaluate the usefulness of enzyme determination in expressed prostatic fluid in identifying patients with a high risk of carcinoma of the prostate; and 2) to attempt to clarify the natural history of carcinoma of the prostate and to determine the value of various clinical procedures to identify the stage of the disease prior to institution of therapy. In an attempt to achieve the first objective, lactic dehydrogenase (LDH) isoenzyme, leucine aminopeptidase, and glucose 6 phosphate dehydrogenase determinations are being carried out in the expressed prostatic fluid of patients; the results of the prostatic fluid studies are being correlated with the clinical and pathologic diagnosis of prostatic pathology. In an attempt to achieve the second objective, patients with a histologic diagnosis of carcinoma of the prostate are subjected to serum acid and alkaline phosphatase determinations and bone x-ray and scan studies. If these are negative or equivocal, pelvic lymph node excisional biopsy is carried out and the nodes subjected to histological study. In addition, random pelvic marrow blood aspiration is performed; the aspirated blood is subjected to acid phosphatase and LDH isoenzyme determination. Simultaneous enzyme determination is carried out on systemic blood. The studies described above are being accomplished at this time. LDH isoenzymes have been determined in 293 specimens. Techniques for the other enzyme determination in prostatic fluid have just been developed. The lymph node-bone marrow studies have been carried out in 20 patients to date.